Merlin is an enchanter often associated with what legendary king?

Merlin, enchanter and wise man in Arthurian legend and romance of the Middle Ages. He appeared in Arthurian legend as an enigmatic figure, fluctuations and inconsistencies in his character being often dictated by the requirements of a particular narrative or by varying attitudes of suspicious regard toward magic and witchcraft. Thus, treatments of Merlin reflect different stages in the development of Arthurian romance itself. Merlin figured as an adviser to Uther Pendragon (King Arthur’s father) and afterward to Arthur himself.

Source: Britannica